I Love Lucy Airs for First Time (1951) READING: reread chapter 7 READING: reread chapter 7 HOMEWORK – DUE TUESDAY 10/20/15 HOMEWORK – DUE TUESDAY 10/20/15 HW-BW 7.1 (Bookwork) CH 7 #’s 5, 7-12 all, 14, 15, 20, 21, 24, all, 34 HW-BW 7.1 (Bookwork) CH 7 #’s 5, 7-12 all, 14, 15, 20, 21, 24, all, 34 HW-WS 12 (Worksheet) (from course website) HW-WS 12 (Worksheet) (from course website) HOMEWORK – DUE THURSDAY 10/22/15 HOMEWORK – DUE THURSDAY 10/22/15 HW-BW 7.2 (Bookwork) CH 7 #’s 39, 42, all, all, 64, 69, 71, 72, 78, 90 HW-BW 7.2 (Bookwork) CH 7 #’s 39, 42, all, all, 64, 69, 71, 72, 78, 90 HW-WS 13 (Worksheet) (from course website) HW-WS 13 (Worksheet) (from course website) Lab Lab Next Monday/Tuesday – EXP 9 Next Monday/Tuesday – EXP 9 Prelab Prelab Next Wednesday/Thursday – EXP 10 Next Wednesday/Thursday – EXP 10

The Nature of Light: Its Wave Nature Light is a form of electromagnetic radiation Light is a form of electromagnetic radiation made of perpendicular waves, one for the electric field and one for the magnetic field made of perpendicular waves, one for the electric field and one for the magnetic field

Light is a form of electromagnetic radiation Light is a form of electromagnetic radiation made of perpendicular waves, one for the electric field and one for the magnetic field made of perpendicular waves, one for the electric field and one for the magnetic field All electromagnetic waves move through space at the same, constant speed All electromagnetic waves move through space at the same, constant speed x 10 8 m/s in a vacuum = the speed of light, c x 10 8 m/s in a vacuum = the speed of light, c The Nature of Light: Its Wave Nature

Characterizing Waves The amplitude is the height of the wave The amplitude is the height of the wave the distance from node to crest or node to trough the distance from node to crest or node to trough

Characterizing Waves Node

Characterizing Waves The amplitude is the height of the wave The amplitude is the height of the wave the distance from node to crest or node to trough the distance from node to crest or node to trough the amplitude is a measure of how intense the light is – the larger the amplitude, the brighter the light the amplitude is a measure of how intense the light is – the larger the amplitude, the brighter the light

Characterizing Waves

The wavelength ( ) is a measure of the distance covered by the wave The wavelength ( ) is a measure of the distance covered by the wave the distance from one crest to the next (or the distance from one trough to the next, or the distance between alternate nodes) the distance from one crest to the next (or the distance from one trough to the next, or the distance between alternate nodes)

Characterizing Waves Node

Characterizing Waves The wavelength ( ) is a measure of the distance covered by the wave The wavelength ( ) is a measure of the distance covered by the wave the distance from one crest to the next (or the distance from one trough to the next, or the distance between alternate nodes) the distance from one crest to the next (or the distance from one trough to the next, or the distance between alternate nodes) For visible light, the wavelength is related to the color of light For visible light, the wavelength is related to the color of light

Characterizing Waves

The frequency ( ) is the number of waves that pass a point in a given period of time The frequency ( ) is the number of waves that pass a point in a given period of time the number of waves = number of cycles the number of waves = number of cycles units are hertz (Hz) or cycles/second = s −1 units are hertz (Hz) or cycles/second = s −1 1 Hz = 1 s −1 1 Hz = 1 s −1 Characterizing Waves

LIGHT!!! wavelength and frequency are INVERSLY proportional wavelength frequency

LIGHT!!! wavelength and energy are INVERSLY proportional wavelength energy

LIGHT!!! energy and frequency are DIRECTLY proportional energy frequency

Wavelength and Frequency Wavelength and frequency of electromagnetic waves are inversely proportional Wavelength and frequency of electromagnetic waves are inversely proportional because the speed of light is constant, if we know wavelength we can find the frequency, and vice versa because the speed of light is constant, if we know wavelength we can find the frequency, and vice versa

Calculate the wavelength of red light (nm) with a frequency of 4.62 x s −1 649 nm

Calculate the wavelength (m) of a radio signal with a frequency of MHz m

Color The color of light is determined by its wavelength or frequency The color of light is determined by its wavelength or frequency White light is a mixture of all the colors of visible light White light is a mixture of all the colors of visible light a spectrum a spectrum RedOrangeYellowGreenBlueViolet RedOrangeYellowGreenBlueViolet When an object absorbs some of the wavelengths of white light and reflects others, it appears colored When an object absorbs some of the wavelengths of white light and reflects others, it appears colored the observed color is predominantly the colors reflected the observed color is predominantly the colors reflected

Types of Electromagnetic Radiation low frequency and energy high frequency and energy Electromagnetic waves are classified by their wavelength

Electromagnetic Spectrum

Interference The interaction between waves is called interference The interaction between waves is called interference When waves interact so that they add to make a larger wave it is called constructive interference When waves interact so that they add to make a larger wave it is called constructive interference waves are in-phase waves are in-phase

Interference The interaction between waves is called interference The interaction between waves is called interference When waves interact so they cancel each other it is called destructive interference When waves interact so they cancel each other it is called destructive interference waves are out-of-phase waves are out-of-phase

Diffraction When traveling waves encounter an obstacle or opening in a barrier that is about the same size as the wavelength, they bend around it – this is called diffraction When traveling waves encounter an obstacle or opening in a barrier that is about the same size as the wavelength, they bend around it – this is called diffraction traveling particles do not diffract traveling particles do not diffract

Diffraction When traveling waves encounter an obstacle or opening in a barrier that is about the same size as the wavelength, they bend around it – this is called diffraction When traveling waves encounter an obstacle or opening in a barrier that is about the same size as the wavelength, they bend around it – this is called diffraction traveling particles do not diffract traveling particles do not diffract The diffraction of light through two slits separated by a distance comparable to the wavelength results in an interference pattern of the diffracted waves The diffraction of light through two slits separated by a distance comparable to the wavelength results in an interference pattern of the diffracted waves An interference pattern is a characteristic of all light waves An interference pattern is a characteristic of all light waves

2-Slit Interference

2-Slit Interference

The Photoelectric Effect Many metals emit electrons when a light shines on them. Many metals emit electrons when a light shines on them. called the photoelectric effect called the photoelectric effect

The Photoelectric Effect

Many metals emit electrons when a light shines on them. Many metals emit electrons when a light shines on them. called the photoelectric effect called the photoelectric effect Classic wave theory said this effect was due to the light energy being transferred to the electron. Classic wave theory said this effect was due to the light energy being transferred to the electron. The energy of a wave is directly proportional to its amplitude and its frequency The energy of a wave is directly proportional to its amplitude and its frequency If the wavelength of light is made shorter, more electrons should be ejected If the wavelength of light is made shorter, more electrons should be ejected Light waves’ intensity made brighter, more electrons should be ejected Light waves’ intensity made brighter, more electrons should be ejected Predicts that if a dim light were used there would be a lag time before electrons were emitted to give the electrons time to absorb enough energy Predicts that if a dim light were used there would be a lag time before electrons were emitted to give the electrons time to absorb enough energy

Experiments showed that a minimum frequency was needed before electrons would be emitted Experiments showed that a minimum frequency was needed before electrons would be emitted called the threshold frequency called the threshold frequency no dependence on intensity no dependence on intensity It was observed that high-frequency light from a dim source caused electron emission without any lag time It was observed that high-frequency light from a dim source caused electron emission without any lag time The Photoelectric Effect: The Problem

Einstein’s Explanation Einstein proposed that the light energy was delivered to the atoms in packets, called quanta or photons Einstein proposed that the light energy was delivered to the atoms in packets, called quanta or photons The energy of a photon of light is directly proportional to its frequency and inversely to wavelength The energy of a photon of light is directly proportional to its frequency and inversely to wavelength the proportionality constant is called Planck’s Constant, (h) and has the value the proportionality constant is called Planck’s Constant, (h) and has the value

Calculate the number of photons in a laser pulse with wavelength 337 nm and total energy 3.83 mJ 6.49x10 15 photons

What is the frequency of radiation required to supply 1.0 x 10 2 J of energy from 8.5 x photons? 1.8x10 7 s -1 or 1.8x10 7 Hz or 18 MHz

Ejected Electrons One photon at the threshold frequency gives the electron just enough energy for it to escape the atom One photon at the threshold frequency gives the electron just enough energy for it to escape the atom binding energy,  binding energy,  When irradiated with a shorter wavelength photon, the electron absorbs more energy than is necessary to escape When irradiated with a shorter wavelength photon, the electron absorbs more energy than is necessary to escape This excess energy becomes kinetic energy of the ejected electron This excess energy becomes kinetic energy of the ejected electron Kinetic Energy = E photon – E binding KE = h − 